In airborne vehicles, such as missiles or unmanned airborne vehicles (“UAV's”) there are sometimes installed payloads, homing heads or sensors whose exterior configuration or form disrupts the aero dynamic efficiency of the airborne vehicle.
For example—
A missile that is launched from the ground to intercept an airborne target (for example—a rocket launched by the enemy, or an enemy plane), might be based on an existing air to air missile. At the nose of such a missile, an optical homing head is mounted, endowed with a dome shaped configuration on its front end (for example—a dome shaped optical window of a sensor that is scanning in search of heat (IR) radiated by the target).
From the aero dynamical aspect—a dome shaped configuration at the nose of a flying body is not efficient, in comparison to a conical or an ogival one. When launching from the ground (or from a mobile platform—vehicle, boat and the like), the launching takes place—practically, at zero speed, and the launched missile has the task to accelerate quickly towards the approaching threat. Under these circumstances the dome shaped configuration of the missile's nose, and its impaired efficiency, as said, from the aero dynamic point of view, constitutes an additional limitation on the ability of the missile to accelerate at the required rate. This, wherein actually, at the earlier stages of the launch and acceleration of the missile in the general direction of the target which has to be intercepted, there exists no real need in these stages to operate the optical homing head (that has the dome shaped configuration and is installed at the front end of the missile). In other words, the aero dynamic limitation stems from the existence of a means that is not being used in the early stages.
Additional missile applications that required delaying the exposure of the missile's homing head are those missiles that are designed as relatively low cost interceptors, in which the budgeting constrains dictate the use of relatively low cost materials, for example—manufacturing the optical dome of the missile homing head from a materials that cannot sustain high temperatures for extended periods of time (in comparison to the highly expensive sapphire type of material as used in advanced air to air missile domes). Therefore in an operational scenario, wherein a low cost ground to air interceptor is desired, the high acceleration constrains dictate either the use of a combination of an acceleration stage with a dome type missile wherein the dome is manufactured from high thermal performance and expensive materials utilizing low cost materials but delaying the exposure of the missile dome while accelerating to the sky.
Hence, in the recent years, devices were developed that split and remove the shroud of the nose cone from an airborne vehicle, in a manner that enables to install in the airborne vehicle (for example, at the head of the ground to air missile cited above), a shroud that is efficient from the aero dynamic aspect, and wherein splitting and removing of that shroud, while exposing the homing head or sensor with the dome shaped configuration at the front end (in accordance with the example that we cited above), only at a later flying stage and when verily its activation is required. Such a removable nose cone prevents over heating of the homing dome, prevents unnecessary use of an accelerator stage, enables manufacturing of the dome from relatively low cost materials, while at the same time, contributes to the achievement of preferable envelope of performance by the missile in terms of maneuverability, angle of attack, sideslip and acceleration.
Thus for example—
A patent application that was published in the USA numbered US 2007/0074636 describes a “jettisonable nose cone and missile with a jettisonable nose cone”. The above cited patent application describes a pyrotechnical device that is characterized by that that it comprises a connecting pin that serves for attaching and fastening the two parts of the nose cone one to the other. Inside the connecting pin, there is integrated the pyrotechnical charge. Detonating the pyrotechnical charge results in breaking the connection pin (inside which, as said, the charge is embedded), and the formation of gas pressure that leads to the splitting and removing of the two parts of the nose cone one from the other.
The device that is described in the above cited patent application is ridden by several disadvantages—
The configuration of the device is illustrated there in FIG. 3, and is based on threads as the connecting and sealing means (see ibid, threads numbered 70 and 71) in a manner that might induce sealing problems and failure resulting from possible leak of gas from the instant the pyrotechnical charge is detonated. This, and more: the configuration of the device that relies on nuts for the task of positioning and fastening (see ibid, devices numbered 26 and 29), dictates the need for the existence of relatively large access openings, formed in the nose cone, that inherently disrupts the aerodynamic continuity of the shroud and disrupts the aero dynamics efficiency of the nose cone.
The configuration of the device that is illustrated there in FIG. 7 might be susceptible as well to several setbacks such as sealing problems and failure due to gas leaks when detonating the pyrotechnic charge, because it relies—as elaborated above, on threads as the connecting and sealing assuring means. This configuration, as used earlier, mandates that relatively large access openings would e formed in the nose cone, thus disrupting the aerodynamic continuity of the surface areas of the shroud.
Moreover—
In this configuration, on detonating the pyrotechnic charge and the separation of the two parts of the nose cone, while moving farther away one from the other, in an essentially circular movement of one from the other, phenomena of clamping may take place. The clamping may take place between the two cylindrical components (see ibid, components 54 and 55), that—upon assembling the nose cone become interlaced one in the other, and this despite of detonation of the pyrotechnic charge and the breaking of the connection element (the pin that in accordance with the technology that is described in the above cited patent application, serves both for connecting and fastening the two parts of the nose cone one to the other and—as well, as the bracket for the pyrotechnic charge that is included in it).
An additional deficiency that might be found in the configuration of the above cited device, constitutes the limitation due to lack of symmetry that is instilled on the structure of the nose cone (as a consequence from the characteristics of the two cylindrical components interlaced in it, one inside the other), which requires separate manufacturing of different components (and increases the costs). Additional deficiencies that might be found in the design illustrated in FIG. 7 (ibid) of said patent application, is its clumsy (and accordingly heavy) structure that might also require a metal structure of the cylindrical components and their bases—because of the impeding danger of forming fractures and fragments upon detonation of the pyrotechnic charge.
The two configurations described in the above cited patent application, even require dedicated tools for the work, e. g. for assembling the components of the various devices (see for example the usage made with non standard nuts with external threads), and also—
The above mentioned publication does not treat the issue of the safety of the pyrotechnic charge. Detonation of the charge, if it would occur inadvertently, due to a mistake or in consequence of a failure—and this if as long as the missile was not inserted in the canister (provided that we are considering a missile dubbed “missile in a box” type), would lead, directly, to active and very powerful separation of the two parts of the nose cone while endangering the people in the vicinity.